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Safe Zinc Recovery from Pyrolysis Char

Safe Zinc Recovery from Pyrolysis Char

By TA News Bureau:

One of the major concerns facing tyre recyclers is how to eliminate environment contaminating zinc from products of waste tyre pyrolysis. Researchers at Poland’s Nicolaus Copernicus University, led by Prof Jerzy P Lukaszewiczhas, has found a way out by developing a process to eliminate zinc from environmental circulation during tyre pyrolysis. They have proposed an alternative solution to transform pyrolytic char into activated carbon. The researchers say that the raw post-pyrolytic chars provide highly energetic fuel for the production of heat and/or electrical energy, which is more competitive than converting them into activated carbon. Such chars should be burned separately with an excess of oxygen in heat/electricity generators. The resulting ash, which has very high zinc content, could be saved for metallurgical conversion to metallic zinc. This could lead to the annual recovery of thousands of tonnes of zinc and/or its derivatives and eliminate them from the environment. In this interview to Tyre Asia, the research head elaborates on their work

Can you explain the main focus of your research on tyre pyrolysis?

It is an obvious fact that the reuse of old tyres is an emerging worldwide problem. The annual number of old tyres, which must be disposed of in an environment-friendly way, is huge. Besides just burning of old tyres for energy purposes, the pyrolysis of tyre rubber is the second main objective of utilization. Traditionally, old rubber from tyres is subjected to heat treatment in a controlled mode. Three basic products are derived out of it: burnable gas, crude oil resembling liquid and a solid by-product i.e. a pyrolytic char. The gas may be utilized on the spot as a heating medium to power the pyrolysis process itself. The pyrolysis oil may be converted to valuable chemicals, including gasoline etc. But what about the char? The char is a real problem since its mass is ca. 40% of the mass of the rubber that is subjected to pyrolysis. Usually, the char has poor surface properties such as very low specific surface area like 40-50 sq metre per gram. Any conversion of such chars into a carbon-type adsorbent (expected surface area is ca. 500-1500 sq metre per gram) is a versatile but expensive process. To my opinion it is senseless due to these technological and economic barriers. From the beginning, our research was focused on finding new recycling scenarios for this troublesome by-product i.e. pyrolytic char. The new pyrolysis concept was developed at Nicolaus Copernicus University of Torun (Poland).

As your process eliminates zinc, a major environmental pollution factor, your research will certainly have worldwide acceptance. However, in terms of cost-effectiveness, how does your process fare compared to other existing processes?

We have proposed a new look on this problem. We decided to treat the char as a source of precious component that is zinc. Its weight content is ca. 1-3% in raw tyre rubber. Our technology is covered by a patent application. It consists of conversion of the pyrolytic char into zinc concentrate having ca. 40% of zinc if recalculated into the elemental weight of the content of this element. Its chemical form is mostly ZnO which is useful in metallurgic industry and other branches. In our process we co-generated heat as a second main product. We are able to generate revenue from this and derive value from the zinc concentrate. Our process eliminates zinc from tyre recycling and removes it from environmental circulation as well. It also generates new products like zinc concentrate and heat.

Can you explain the advantages of transformation of pyrolytic char into activated carbon?

I need to present my previous argument again: Our process eliminates zinc from the tyre utilization process and from the environmental circulation as well. It also gives new products like zinc concentrate and heat. The cost of zinc concentrate and the heat generation are countable. The environmental benefits are generally hard to measure but the situation of less zinc emission to the environment is welcomed by everybody everywhere. The problem of zinc polluting soils around cement plants that burn old tyres in mass quantities is known worldwide, including in my country Poland. Besides polluting our living environment, we are also losing zinc which is a limited resource.

What are the applications where the activated carbon is widely used?

It can be a supplement at every tyre pyrolysis installations which is producing mass amounts of the char. There is no territorial limitation unless some administrative regulations are against it. I would recommend our technological concept to the manufacturers of tyre pyrolysis installations, too.

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